Question

Select the correct sequence in gene expression in eukaryotes.

• A. DNA \(\rightarrow\) mRNA \(\rightarrow\) hnRNA \(\rightarrow\) Protein
• B. DNA \(\rightarrow\) hnRNA \(\rightarrow\) mRNA \(\rightarrow\) Protein
• C. hnRNA \(\rightarrow\) DNA \(\rightarrow\) mRNA \(\rightarrow\) Protein
• D. DNA \(\rightarrow\) Protein \(\rightarrow\) mRNA

Hint:

hnRNA is the unprocessed primary transcript that becomes mature mRNA after splicing.

Answer 1

The Correct Option is B

Gene expression is the process by which genetic information stored in DNA is utilized to synthesize proteins. In eukaryotes, gene expression occurs in multiple stages.
Step 1: Transcription
• DNA acts as template.
• RNA polymerase synthesizes a primary RNA transcript.
• This initial transcript is called hnRNA (heterogeneous nuclear RNA). hnRNA is immature and cannot directly participate in protein synthesis.
Step 2: RNA Processing The hnRNA undergoes:
• Capping at 5' end
• Tailing at 3' end
• Splicing to remove introns After processing, mature mRNA is formed.
Step 3: Translation
• Mature mRNA moves to ribosomes.
• Amino acids are assembled according to codon sequence.
• Protein synthesis occurs. Thus, the correct sequence is: \[ \text{DNA} \rightarrow \text{hnRNA} \rightarrow \text{mRNA} \rightarrow \text{Protein} \] Option analysis:
• Option (A): Incorrect because hnRNA forms before mature mRNA.
• Option (B): Correct
• Option (C): Incorrect order
• Option (D): Incorrect because mRNA formation precedes protein synthesis. Therefore: \[ \boxed{\text{(B)}} \]